Method and system for dehumidification and refrigerant pressure control

ABSTRACT

A method for dehumidification and controlling system pressure in a refrigeration system includes providing a refrigeration system having a compressor, a condenser and an evaporator connected in a closed refrigerant loop. Each of the condenser and evaporator have a plurality of refrigerant circuits. A first heat transfer fluid is flowed over the condenser and a second heat transfer fluid is flowed over the evaporator. At least one of the refrigerant circuits of the condenser is isolated to provide a decreased amount of heat transfer area within the condenser and to increase the refrigerant pressure within the refrigeration system when the refrigerant pressure within the refrigeration system is at or below a predetermined pressure. At least one of the refrigerant circuits of the evaporator is isolated to dehumidify and maintain the temperature of the second heat transfer fluid at or above a predetermined temperature when dehumidification is required.

BACKGROUND

The present invention relates generally to heating, ventilation and airconditioner systems (HVAC), including systems that can dehumidify air.

An HVAC system generally includes a closed loop refrigeration systemwith at least one evaporator, at least one condenser and at least onecompressor. As the refrigerant travels through the evaporator, itabsorbs heat from a heat transfer fluid and changes from a liquid to avapor phase. After exiting the evaporator, the refrigerant proceeds to acompressor, then a condenser, then an expansion valve, and back to theevaporator, repeating the loop. The heat transfer fluid to be cooled(e.g. air) passes through the evaporator in a separate fluid channel andis cooled by the evaporation of the refrigerant. The heat transfer fluidcan then be sent to a distribution system for cooling the spaces to beconditioned, or it can be used for other refrigeration purposes.

Other refrigeration purposes may include dehumidification.Dehumidification of air in HVAC systems can occur through the use of theevaporator in the cooling mode. One drawback to using just an evaporatorfor dehumidification is an excess reduction in air temperature thatresults, which is commonly referred to as overcooling. Overcoolingoccurs when air that is subject to dehumidification is cooled to atemperature that is below the desired temperature of the air.Overcooling is a particular problem when dehumidification is required ina room that is already relatively cool and does not require additionalcooling. Overcooling generally involves air temperatures ofapproximately 50° F. to 55° F. or lower.

The problem of overcooling has been addressed in one solution byutilization of a reheat coil in one solution. Air that is overcooled bythe evaporator is passed over the reheat coil in order to increase thetemperature of the overcooled, dehumidified air to a desiredtemperature. The reheat coil can be heated by diverting hot refrigerantthrough the reheat coil when dehumidification is required. Reheat mayalso be provided by alternate heat sources, such as electric heat or gasheat. The reheat coil system for providing heat to the dehumidified,overcooled air has several drawbacks including the requirement ofadditional equipment and/or piping and/or additional energy input.

Another dehumidification method known in the art is disclosed in U.S.Pat. No. 4,182,133 (the '133 patent). The '133 patent is directed to adehumidification method that controls refrigerant flow through circuitswithin the indoor coil of an air conditioning/heat pump unit. The '133patent system, when providing dehumidification, has a header thatdistributes the refrigerant across several circuits within the indoorcoil. At the opposite end of the indoor coil, the outlets of the variouscircuits of the coil are allowed to flow into a single common vaporheader. The header at the inlet of the indoor coil contains a solenoidvalve that may be closed to prevent refrigerant flow to one or more ofthe circuits within the coil. The '133 patent system operates such thatwhen humidity reaches a certain level, the valve in the inlet header isclosed in order to limit the number of available circuits forrefrigerant flow. The area of the indoor coil that remains in the activecircuit and receives refrigerant flow, experiences an increase inrefrigerant flow through a given heat transfer area. The increased flowof refrigerant results in a greater amount of moisture being removedfrom the air in that portion of the indoor coil. One drawback of the'133 patent system is that the dehumidified air is not reheated and maybe overcooled. Another drawback of the '133 patent system is that theinlet header does not distribute flow across the circuits of theevaporator, leading to uneven phase distribution of refrigerant acrossthe evaporator heat exchanger. Another drawback of the '133 patentsystem is that it is nearly impossible for a properly functioning systemto deliver supply air that has not been sensibly cooled.

One type of HVAC system is a split system where there is an indoor unitor heat exchanger, which is generally the evaporator, and an outdoorunit or heat exchanger, which is generally the condenser. Often, theoutdoor unit is placed outdoors and is subject to outdoor ambientconditions, particularly temperature. When the outdoor ambienttemperature falls, the amount of heat being removed from the refrigerantin the condenser increases. The increased heat removal in the condensercan result in a decrease in the refrigerant pressure at the suction lineto the compressor, commonly referred to as head pressure. The decreasein head pressure results in a lowering of the temperature of therefrigerant at the evaporator. When the temperature of the refrigerantat the evaporator becomes too low, icing of the evaporator can occur.Icing is a condition when the temperature at the exterior of the systemis sufficiently low to freeze water present in the atmosphere. The iceformed by the water frozen on the surface reduces the available heattransfer surface and eventually prevents the proper operation of theHVAC system by inhibiting heat transfer and/or damaging systemcomponents.

Some attempts to address the problem of icing have utilized the controlof system pressure. In one approach, a variable speed condenser fan or aplurality of condenser fans having independent controls are used tocontrol airflow over the condenser coil. As the amount of air passingover the coil decreases, the amount of heat transfer taking place at thecoil decreases. Therefore, the temperature of the refrigerant in thecondenser and the pressure of the system increase to allow the indoorcoil to cool the air without icing problems. The use of the variablespeed condenser fan or a plurality of condenser fans having independentcontrols has the drawback that it is expensive and requires complicatedwiring and controls.

An alternate approach for the problem of low system pressure or icing isa parallel set of condensers in the refrigerant cycle, as described inU.S. Pat. No. 3,631,686 (the '686 patent). In the '686 patent system aparallel set of refrigerant condensers allows for two modes ofoperation. One mode of operation allows refrigerant to flow from onlyone of the refrigerant condensers. During this mode of operation, thecondenser that does not permit the flow of refrigerant fills with liquidrefrigerant. Because of this flooding, there is a reduction in theeffective surface area of the condenser. The reduced surface areathereby reduces the ability of the condenser to remove heat from therefrigerant. Therefore, the temperature of the refrigerant in thecondenser and the head pressure of the system increase, allowing theindoor coil to cool the air without icing. The use of parallelrefrigerant condensers has the drawback that it requires an additionalcondenser coil and additional piping, thereby increasing the space andcost required for installation. Another drawback associated withrefrigerant flooding of the condenser coil is the resultant decrease insystem capacity. Refrigerant normally available in a properly operatingsystem is trapped in the condenser coil and not available to thecompressor, thereby decreasing system capacity.

Therefore, what is needed is a method and system for dehumidificationthat dehumidifies air without overcooling, provides control of therefrigerant pressure and provides a system that can be retrofitted intoexisting systems without the drawbacks discussed above.

SUMMARY

The present invention is directed to a method for dehumidification andcontrolling system pressure in a refrigeration system. The methodcomprises the step of providing a refrigeration system having acompressor, a condenser and an evaporator connected in a closedrefrigerant loop. Each of the condenser and evaporator have a pluralityof refrigerant circuits. A first heat transfer fluid is flowed over thecondenser. A second heat transfer fluid is flowed over the evaporator.The flow of refrigerant is controlled in the refrigerant circuits in thecondenser to control the amount of heat transfer between refrigerant inthe condenser and the first heat transfer fluid. The flow of refrigerantis controlled in the refrigerant circuits in the evaporator to controlan amount of heat transfer between refrigerant in the evaporator and thesecond heat transfer fluid. At least one of the refrigerant circuits ofthe condenser is isolated to provide a decreased amount of heat transferarea within the condenser and to increase the refrigerant pressurewithin the refrigeration system when the refrigerant pressure within therefrigeration system is at or below a predetermined pressure. At leastone of the refrigerant circuits of the evaporator is isolated todehumidify the second heat transfer fluid and maintain the temperatureof the second heat transfer fluid at or above a predeterminedtemperature when dehumidification is required.

Another embodiment of the invention includes a method fordehumidification and controlling refrigerant pressure in a heating,ventilation and air conditioning system. The method comprises providinga closed loop refrigerant system comprising a compressor, a condenserand an evaporator. Each of the condenser and evaporator having aplurality of refrigerant circuits configured and disposed to allowisolation of at least one of the refrigerant circuits from refrigerantflow. Pressure is measured at a predetermined location in therefrigeration system. An operational mode is determined for therefrigeration cycle. The operational mode is selected from the groupconsisting of cooling and dehumidification. At least one of therefrigeration circuits in the condenser is isolated from refrigerantflow when the measured pressure at the predetermined location is equalto or less than a predetermined pressure. A first set of refrigerantcircuits in the evaporator is isolated from flow of refrigerant from thecondenser when the operational mode is dehumidification. Flow ofrefrigerant is permitted from the condenser to both the first and secondset of refrigerant circuits in the evaporator when the operational modeis cooling. The refrigerant pressure is increased by isolation of atleast one of the refrigerant circuits in the condenser from refrigerantflow until the measured pressure is greater than the predeterminedpressure.

Another embodiment of the invention includes a heating, ventilation andair conditioning system. The system comprises a compressor, a condenserarrangement and an evaporator arrangement. The condenser arrangementcomprises a plurality of circuits arranged into a first and second setof circuits, and a valve arrangement configured and disposed to isolatethe first set of circuits of the condenser arrangement when therefrigerant pressure is below a predetermined pressure. The evaporatorarrangement comprises a plurality of circuits arranged into a first andsecond set of circuits, at least one distributor configured todistribute and deliver refrigerant to each circuit of the plurality ofcircuits in the evaporator, and a valve arrangement configured anddisposed to isolate the first set of circuits of the evaporatorarrangement from refrigerant flow in a dehumidification operation of theHVAC system.

The present invention provides an inexpensive method and system tocontrol head pressure, while also being capable of reheatingdehumidified air. The method and system requires little or no additionalpiping in order to implement the method and system in an existing HVACunit. The system requires less in materials and therefore costs lessthan systems having separate components, such as separate reheat coils.

Another advantage of the present invention is that the air conditioningor heat pump unit can operate at lower outdoor ambient temperatures byproviding an increase in system pressure to avoid icing of the systemcomponents.

Another advantage of the present invention is that the system and methoddistributes refrigerant substantially uniformly across the evaporator toprovide substantially uniform refrigerant phase distribution and heatexchange across the evaporator.

Another advantage of the present invention is that the system can reheatair and control head pressure without the need for a separate airflowsystem.

Another advantage of the system is that the simultaneous control of thehead pressure of the system and reheating of the air duringdehumidification permits the system to be operated in a manner thatincreases the efficiency and reliability of the system, whilemaintaining greater control of the temperature and humidity of theconditioned air.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a refrigeration or HVAC system.

FIG. 2 schematically illustrates one embodiment of an evaporator andpiping arrangement of the present invention.

FIG. 3 schematically illustrates another embodiment of an evaporator andpiping arrangement of the present invention.

FIG. 4 schematically illustrates further embodiment of an evaporator andpiping arrangement of the present invention.

FIG. 5 schematically illustrates one embodiment of a condenser andpiping arrangement of the present invention.

FIG. 6 schematically illustrates another embodiment of a condenser andpiping arrangement of the present invention.

FIG. 7 schematically illustrates one embodiment of a refrigeration orHVAC system according to the present invention.

FIG. 8 schematically illustrates another embodiment of a refrigerationor HVAC system according to the present invention.

FIG. 9 schematically illustrates a refrigeration or HVAC system ofanother embodiment of the present invention.

FIG. 10 schematically illustrates a refrigeration or HVAC system of afurther embodiment of the present invention.

FIG. 11 illustrates a control method of the present invention.

FIG. 12 illustrates a control method of another embodiment of thepresent invention.

FIG. 13 illustrates a control method of a further embodiment of thepresent invention.

FIG. 14 illustrates a control method of a further embodiment of thepresent invention.

FIG. 15 illustrates a control method of a further embodiment of thepresent invention.

FIG. 16 illustrates a control method of a further embodiment of thepresent invention.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION

FIG. 1 illustrates a HVAC, refrigeration, or chiller system 100.Refrigeration system 100 includes a compressor 130, a condenser 120, andan evaporator 110. The compressor 130 compresses a refrigerant vapor anddelivers it to the condenser 120 through compressor discharge line 135.The compressor 130 is preferably a reciprocating or scroll compressor,however, any other suitable type of compressor can be used, for example,screw compressor, rotary compressor, and centrifugal compressor. Therefrigerant vapor delivered by the compressor 130 to the condenser 120enters into a heat exchange relationship with a first heat transferfluid 150, preferably air, and undergoes a phase change to a refrigerantliquid as a result of the heat exchange relationship with the first heattransfer fluid 150. The first heat transfer fluid 150 is moved by use ofa fan 170, which moves the first heat transfer fluid 150 through thecondenser 120 in a direction perpendicular the cross section of thecondenser 120. In a preferred embodiment, the refrigerant vapordelivered to the condenser 120 enters into a heat exchange relationshipwith air as the first heat transfer fluid 150. The refrigerant leavesthe condenser through the condenser discharge line 140 and is deliveredto an evaporator 110 after passing through an expansion device (notshown). The evaporator 110 includes a heat-exchanger coil. The liquidrefrigerant in the evaporator 110 enters into a heat exchangerelationship with a second heat transfer fluid 155 to lower thetemperature of the second heat transfer fluid 155. The second heattransfer fluid 155, preferably air, is moved by use of a blower 160,which moves the second heat transfer fluid 155 through evaporator 110 ina direction perpendicular the cross section of the evaporator 110.Although FIG. 1 depicts the use of a blower 160 and fan 170, any fluidmoving means may be used to move fluid through the evaporator andcondenser 120. In a preferred embodiment, the refrigerant vapordelivered to the evaporator 110 enters into a heat exchange relationshipwith air as the second heat transfer fluid 155. The refrigerant liquidin the evaporator 110 undergoes a phase change to a refrigerant vapor asa result of the heat exchange relationship with the second heat transferfluid 155. The vapor refrigerant in the evaporator 110 exits theevaporator 110 and returns to the compressor 130 through a suction line145 to complete the cycle. The conventional refrigerant system 100includes many other features that are not shown in FIG. 1. Thesefeatures have been purposely omitted to simplify the figure for ease ofillustration.

FIG. 2 illustrates a partitioned evaporator 200 according to oneembodiment of the present invention. The inlet of the partitionedevaporator 200 includes a condenser discharge line 140 from thepartitioned condenser 500 (see FIG. 7), a first and second thermostaticexpansion valve (TXV valve) 260 and 265, an isolation valve 250, and afirst and second distributor 240 and 245. Although FIGS. 2-4 and 7-9illustrate TXV valves, any suitable pressure reduction or expansiondevice may be used to control refrigerant flow, such as a fixed orifice.The first TXV valve 260 and the isolation valve 250 are positionedbetween condenser discharge line 140 and the first distributor 240. Thesecond TXV valve 265 is positioned between the condenser discharge line140 and the second distributor 245. The partitioned evaporator 200includes refrigerant circuits 210. Although refrigerant circuits 210 areshown as curved lines in FIGS. 2-4, the shape shown is merely schematicand any suitable configuration of refrigerant circuit 210 can be used.Refrigerant circuits 210 can include any configuration of device capableof transferring heat. An example of a suitable device includes a finnedtube. The number of refrigerant circuits 210 may be any number ofrefrigerant circuits 210 that provide sufficient heat transfer tomaintain operation of the partitioned evaporator 200 within therefrigeration system 100. The partitioned evaporator 200 is preferablypartitioned into a first and second evaporator portions 220 and 230. Thefirst and second evaporator portion 220 and 230 may be sized in anyproportion. For example, the first evaporator portion 220 may be 60% ofthe size of the partitioned evaporator 200 and the second evaporatorportion 230 may be 40% of the size of the partitioned evaporator 200 orthe first evaporator portion 220 may be 40% of the size of thepartitioned evaporator 200 and the second evaporator portion 230 may be60% of the size of the partitioned evaporator 200 or the first andsecond evaporator portions 220 and 230 may each represent 50% of thesize of the partitioned evaporator 200.

Although FIG. 2 shows the partitioned evaporator 200 as only includingtwo portions, any number of portions may be used in the presentinvention. Where more than two evaporator portions are present, the flowmay be regulated to each of the portions. For example, in the embodimentwhere the evaporator is split into three portions, two of the threeportions include valve arrangements that allow independent isolation ofeach of these portions. One or both of the two portions with valvearrangements may be isolated, dependent on a signal from a controllerand/or sensor. The outlet of the partitioned evaporator 200 includesfirst and second discharge headers 270 and 275, first and secondthermostatic expansion valve bulbs (TXV bulbs) 264 and 269, and anevaporator discharge line 145 to the compressor 130. The first dischargeheader 270 receives refrigerant from the refrigerant circuits 210 in thefirst evaporator portion 220. The second discharge header 275 receivesrefrigerant from the refrigerant circuits 210 present in the secondevaporator portion 230. The first TXV bulb 264 is positioned between thefirst discharge header 270 and the evaporator discharge line 145. Thefirst TXV bulb 264 senses the temperature of the refrigerant leaving thefirst discharge header 270 and compares the temperature of therefrigerant to the temperature of the refrigerant at the first TXV valve260 through line 262. The flow of refrigerant through the first TXVvalve 260 is increased as the temperature difference at the first TXVbulb 264 and the first TXV valve 260 increases. The flow of refrigerantthrough the first TXV valve 260 is decreased as the temperaturedifference at the first TXV bulb 264 and the first TXV valve 260decreases. The second TXV valve 265 operates in the same manner withrespect to the refrigerant discharge from the second discharge header275 and communicates the temperature measurement to the second TXV valve265 through line 267. The isolation valve 250 allows the firstevaporator portion 220 of the partitioned evaporator 200 to be isolatedfrom flow of refrigerant. In one embodiment, to accommodate an increasedflow of refrigerant to the second evaporator portion 230, as discussedin detail below, the size of the second TXV valve 265 (i.e., the amountof flow permitted through the valve) is greater than the size of thefirst TXV valve 260.

During operation of the refrigeration system 100 in cooling mode,refrigerant flows from the partitioned condenser 500 to the partitionedevaporator 200 through condenser discharge line 140. The flow is splitinto two refrigerant flow paths prior to entering the partitionedevaporator 200. Although FIG. 2 shows two paths leading to the first andsecond distributors 240 and 245, the refrigerant flow may be split intotwo or more paths. If the system is in a cooling only mode, isolationvalve 250 is open and refrigerant is permitted to flow into both thefirst and second evaporator portions 220 and 230 of the partitionedevaporator 200. The two refrigerant flow paths are further split by afirst and second distributor 240 and 245 into a plurality of lines,corresponding to the individual refrigerant circuits 210. The first andsecond distributors 240 and 245 may include any arrangement thatdistributes the refrigerant to the individual refrigerant circuits 210within the partitioned evaporator 200. The first and second distributors240 and 245 can preferably distribute the refrigerant to provide uniformphase distribution across the refrigerant circuits 210 of thepartitioned evaporator 200 and, thus, provide substantially uniform heattransfer. The first and second distributors 240 and 245 also may includecombinations of distributor tubes and orifices to provide the uniformrefrigerant flow. The refrigerant flows into the refrigerant circuits210 of first and second evaporator portions 220 and 230. The refrigerantcircuits 210 permit the refrigerant to enter into a heat transferrelationship with the second heat transfer fluid 155 to cool the secondheat transfer fluid 155. Due to the heat transfer with the second heattransfer fluid 155, the refrigerant entering the first and seconddischarge headers 270 and 275 has a higher temperature than thetemperature of the refrigerant entering the partitioned evaporator 200.The refrigerant then travels from the first and second discharge headers270 and 275 past the first and second TXV bulbs 264 and 269. The TXVbulbs 264 and 269 sense the temperature of the refrigerant leaving thepartitioned evaporator 200 and communicate the temperature to the firstand second TXV valves 260 and 265 in order to determine the appropriaterefrigerant flow into the partitioned evaporator 200. After travelingpast the first and second TXV bulbs 264 and 269, the refrigerant isdelivered to the compressor 130 through evaporator discharge line 145.

If the system shown in FIG. 2 is operated in a dehumidification mode,isolation valve 250 is closed and refrigerant flow to the firstevaporator portion 220 is prevented. The refrigerant flow in the secondevaporator portion 230 occurs substantially as described above withrespect to evaporator portion 220 in cooling mode. However, the flow ofrefrigerant to the first evaporator portion 220 is prevented. Since flowto the first evaporator portion 220 is prevented, the flow to the secondevaporator portion 230 is increased. Due to the increased flow of therefrigerant through the second evaporator portion 230, the amount ofheat transfer per unit area is increased and the dehumidification perunit area is likewise increased. Therefore, when the second heattransfer fluid 155 is passed through the second evaporator portion 230the second heat transfer fluid 155 is cooled and dehumidified, and thesecond heat transfer fluid 155 passing through the first evaporatorportion 220 remains substantially unchanged in temperature and humidityfrom inlet to outlet. The second heat transfer fluid 155 passed throughthe second evaporator portion 230 is generally overcooled and the secondheat transfer fluid 155 passed through the first evaporator portion 220is about ambient temperature. The ambient second heat transfer fluid 155that passes though the first evaporator portion 220 mixes with thesecond heat transfer fluid 155 passing through the second evaporatorportion 230 and produces an outlet heat transfer fluid, preferably air,that is dehumidified and not overcooled. As shown in FIG. 2, the flow ofthe second heat transfer fluid 155 is substantially perpendicular to thecross-section of the evaporator. The direction of the flow is such thatthe heat transfer fluid 155 flows simultaneously through firstevaporator portion 220 and second evaporator portion 230. A singlesystem for moving the second heat transfer fluid 155, such as an airblower 160, can be used to simultaneously move air through firstevaporator portion 220 and second evaporator portion 230.

FIG. 3 illustrates a partitioned evaporator 200 according to anotherembodiment of the present invention. The inlet of the partitionedevaporator 200 includes substantially the same arrangement of componentsas FIG. 2, including a condenser discharge line 140 from the partitionedcondenser 500, first and second TXV valves 260 and 265, and first andsecond distributors 240 and 245. FIG. 3 further includes check valve 255that prevents flow of refrigerant into evaporator portion 220 and allowsflow of refrigerant out of evaporator portion 220. The partitionedevaporator 200 includes substantially the same arrangement ofrefrigerant circuits 210 as FIG. 2. The outlet of the partitionedevaporator 200 shown in FIG. 3 includes the first and second dischargeheaders 270 and 275, first and second TXV bulbs 264 and 269, anevaporator discharge line 145 to the compressor 130 and a firstdischarge header discharge line 310 to a 3-way valve 910 (see FIG. 8).The first discharge header 270 receives refrigerant from the refrigerantcircuits 210 present in the first evaporator portion 220. The seconddischarge header 275 receives refrigerant from the circuits 210 presentin the second evaporator portion 230. The first TXV bulb 264 ispositioned on the first discharge header discharge line 310. The firstTXV bulb 264 senses the temperature of the refrigerant leaving the firstdischarge header 270 and compares the temperature of the refrigerant tothe temperature of the refrigerant at the first TXV valve 260 throughline 262. The flow of refrigerant through the first TXV valve 260 isincreased as the temperature difference at the first TXV bulb 264 andthe first TXV valve 260 increases. The flow of refrigerant through thefirst TXV valve 260 is decreased as the temperature difference at thefirst TXV bulb 264 and the first TXV valve 260 decreases. The second TXVvalve 265 operates in the same manner with respect to the refrigerantdischarge from the second discharge header 275 and communicates thetemperature measurement to the second TXV valve 265 through line 267.The use of independent first and second TXV valves 260 and 265 allowsindependent control of the flow through each of the portions of thepartitioned evaporator 200.

During operation in cooling mode, FIG. 3, like in the system shown inFIG. 2, refrigerant flows from the partitioned condenser 500 into thepartitioned evaporator 200 through condenser discharge line 140, throughthe valve arrangement, including the first and second TXV valves 260 and265, and into the first and second distributors 240 and 245. Therefrigerant circuits 210 permit the refrigerant to enter into a heattransfer relationship with the second heat transfer fluid 155 that flowsthrough the circuits perpendicular to the cross-section shown in FIG. 3.Due to the heat transfer with the second heat transfer fluid 155, therefrigerant entering the first and second discharge headers 270 and 275has a higher temperature than the temperature of the refrigerantentering the partitioned evaporator 200. The refrigerant flow throughdischarge line 310 from the first discharge header 270 travels past thefirst TXV bulb 264 and travels to a 3-way valve 910, discussed ingreater detail below. The refrigerant flow through evaporator dischargeline 145 from the second discharge header 275 travels past the secondTXV bulb 269 to the compressor 130.

During dehumidification mode, refrigerant flow in the first evaporatorportion 220 is received from the 3-way valve 910 through the dischargeline 310, as discussed in greater detail below. The flow from the 3-wayvalve 910 is hot refrigerant gas taken from the compressor discharge.The flow from the 3-way valve 910 travels through the discharge line 310in the direction of the first discharge header 270. From the firstdischarge header 270, the hot refrigerant gas enters the firstevaporator portion 220 and travels through circuits 210 to the firstdistributor 240. The refrigerant in refrigerant circuits 210 of thefirst evaporator portion 220 can heat the second heat transfer fluid 155as the fluid passes over the refrigerant circuits 210. The hotrefrigerant gas is at least partially condensed to a liquid in the firstevaporator portion 220. The refrigerant, which is at least partiallycondensed to a liquid, then bypasses the TXV valve 260 by travelingthrough check valve 255. The flow through check valve 255 combines withthe condenser discharge line 140 and enters the second evaporatorportion 230 through the second distributor 245. Due to the increasedflow of the refrigerant through the second evaporator portion 230, theamount of heat transfer per unit area is increased and thedehumidification per unit area is likewise increased. Simultaneously,hot gas refrigerant entering the first evaporator portion 220 of thepartitioned evaporator 200 provides an increase in the temperature ofthe first evaporator portion 220 due to the at least partial condensingof the hot gas. Therefore, the second heat transfer fluid 155 passingthrough the second evaporator portion 230 is cooled and dehumidified,while the second heat transfer fluid 155 passing through the firstevaporator portion 220 is heated by the hot gas refrigerant from thecompressor discharge. This second heat transfer fluid 155 simultaneouslyis circulated through first and second evaporator portions 220 and 230by a fluid moving system, such as an air blower 160, when the secondheat transfer fluid 155 is air. The warmer second heat transfer fluid155 that passes though the first evaporator portion 220 mixes with thesecond heat transfer fluid 155 passing through the second evaporatorportion 230 and produces an outlet heat transfer fluid, preferably air,that is dehumidified and not overcooled.

FIG. 4 illustrates a partitioned evaporator 200 according to a furtherembodiment of the present invention. The inlet of the partitionedevaporator 200 includes a condenser discharge line 140 from thepartitioned condenser 500, a bypass line 410 (see FIG. 9) from thedischarge of the compressor 130, first and second TXV valves 260 and265, isolation valve 250, and first and second distributors 240 and 245.The first TXV valve 260 and the isolation valve 250 are positionedbetween condenser discharge line 140 and the first distributor 240. Thebypass line 410 connects to the line between the first TXV valve 260 andthe first distributor 240. Bypass line 410 is from the discharge of thecompressor 130 and includes a flow restriction valve 430 and a bypassvalve 440. While FIG. 4 shows both a flow restriction valve 430 and abypass valve 440, either one or both of valves 430 and 440 may bepresent. The isolation valve 250 is positioned between the condenserdischarge line 140 and the first TXV valve 260. The second TXV valve 265is positioned between the condenser discharge line 140 and the seconddistributor 245. The partitioned evaporator 200 includes substantiallythe same arrangement of refrigerant circuits 210 as shown in FIG. 2. Theoutlet of the partitioned evaporator 200 includes first and seconddischarge headers 270 and 275, first and second TXV bulbs 264 and 269,and evaporator discharge line 145 to the compressor 130. The firstdischarge header 270 receives refrigerant from the refrigerant circuits210 present in the first evaporator portion 220. The second dischargeheader 275 receives refrigerant from the refrigerant circuits 210present in the second evaporator portion 230. The first TXV bulb 264 ispositioned between the first discharge header 270 and the evaporatordischarge line 145. The first TXV bulb 264 senses the temperature of therefrigerant leaving the first discharge header 270 and compares thetemperature of the refrigerant to the temperature of the refrigerant atthe first TXV valve 260 through line 262. The flow of refrigerantthrough the first TXV valve 260 is increased as the temperaturedifference at the first TXV bulb 264 and the first TXV valve 260increases. The flow of refrigerant through the first TXV valve 260 isdecreased as the temperature difference at the first TXV bulb 264 andthe first TXV valve 260 decreases. The second TXV valve 265 operates inthe same manner with respect to the refrigerant discharge from thesecond discharge header 275 and communicates the temperature measurementto the second TXV valve 265 through line 267. The isolation valve 250allows the first evaporator portion 220 of the partitioned evaporator200 to be isolated from flow of refrigerant. In one embodiment, toaccommodate the increased flow of refrigerant to the second evaporatorportion 230, the size of the second TXV valve 265 (i.e., the amount offlow permitted through the valve) is greater than the size of the firstTXV valve 260.

During operation in cooling mode, FIG. 4, like in the system shown inFIG. 2, refrigerant flows from the partitioned condenser 500 into therefrigerant circuits 210 of the partitioned evaporator 200 through thecondenser discharge line 140, through the valve arrangement, includingthe first and second TXV valves 260 and 265, and the isolation valve250, and into the first and second distributors 240 and 245. In coolingmode, substantially no flow of refrigerant takes place into or out ofthe bypass line 410 because the bypass valve 440 is closed. Theoperation of the refrigerant circuits 210 and the outlet of thepartitioned evaporator 200, including the first and second headers 270and 275, the first and second TXV bulbs 264 and 269 and the evaporatordischarge line 145 to the compressor is substantially similar to theoperation described above with respect to FIG. 2.

However, if the system shown in FIG. 4 is in dehumidification mode,isolation valve 250 is closed and refrigerant flow to the first TXVvalve 260 is prevented. Refrigerant flow from the discharge of thecompressor 130 through bypass line 410 flows into the first distributor240 and into the first evaporator portion 220. The hot gas refrigerantentering the first evaporator portion 220 of the partitioned evaporator200 provides an increase in the temperature of the first evaporatorportion 220. Due to the increased flow of the refrigerant through thesecond evaporator portion 230 by closing isolation valve 250, the amountof heat transfer per unit area is increased and the dehumidification perunit area is likewise increased. Therefore, the second heat transferfluid 155 passing through the second evaporator portion 230 is cooledand dehumidified, while the second heat transfer fluid 155 passingthrough the first evaporator portion 220 is warmed by the hot gasrefrigerant from the compressor discharge. The second heat transferfluid 155 simultaneously is circulated through first and secondevaporator portions 220 and 230 by a fluid moving system, such as ablower 160. The warmer second heat transfer fluid 155 that passes thoughthe first evaporator portion 220 mixes with the second heat transferfluid 155 passing through the second evaporator portion 230 and producesan outlet heat transfer fluid, preferably air, that is dehumidified andnot overcooled.

Although the partitioned evaporator 200 has been illustrated ascontaining two evaporator portions 220 and 230, the partitionedevaporator 200 is not limited to two portions. Any number of portionsmay be used, so long as one or more of the portions includes valving toisolate the respective portion from refrigerant flow.

In another embodiment, refrigerant circuits 210 may also be isolatedindividually within the first and/or second distributor. The refrigerantcircuits 210 may be isolated with flow blocking means or flowrestriction means on first and second distributors 240 and 245. In thisembodiment, a controller is used to determine the number of circuitsisolated. The number of refrigerant circuits 210 isolated relates to theamount of cooling and/or heating of dehumidified air required and may beadjusted by the controller.

FIG. 5 illustrates a partitioned condenser 500 according to oneembodiment of the invention. Partitioned condenser 500 includes aplurality of heat transfer circuits 510. The heat transfer circuits 510are preferably partitioned into a first condenser portion 520 and asecond condenser portion 530. Although heat transfer circuits 510 in thepartitioned condenser 500 are shown as lines in FIGS. 5-6, the shapeshown is merely schematic. Heat transfer circuits 510 are preferably ofany suitable configuration capable of transferring heat. An example of asuitable device includes a finned tube. The first and second condenserportions 520 and 530 may be sized in any proportion. For example, thefirst condenser portion 520 may be 60% of the size of the partitionedcondenser 500 and the second condenser portion 530 may be 40% of thesize of the partitioned condenser 500 or the first condenser portion 520may be 40% of the size of the partitioned condenser 500 and the secondcondenser portion 530 may be 60% of the size of the partitionedcondenser 500 or the first and second condenser portions 520 and 530 mayeach represent 50% of the size of the partitioned condenser 500. Whenthe first and second condenser portions 520 and 530 are different sizes,e.g., 60%/40% split, the refrigerant flow may be directed in any mannerthat provides efficient condenser 500 operation. For example, the firstcondenser portion 520 may constitute 60% of the size of the partitionedcondenser 500 and the second condenser portion 530 may constitute 40% ofthe partitioned condenser 500. When desirable, the flow may be directedto either the 60% portion or the 40% portion and the designation of thefirst and second condenser portions 520 and 530 may be alternated to theisolated portion that provides the desired condenser 500 operation.

Inlet flow 550 includes vaporous refrigerant from the compressor 130.Inlet flow 550 enters the partitioned condenser 500 and travels throughthe heat transfer circuits 510, where the heat transfer circuits 510 canenter into a heat exchange relationship with a heat transfer fluid suchas air. The partitioned condenser 500 preferably has two condenserportions; however, the present invention is not limited to two condenserportions. The present invention may include more than two condenserportions. Where more than two condenser portions are present, the flowmay be regulated to each of the portions. For example, in an embodimentwhere the condenser is split into three portions, two of the threeportions include valve arrangements that allow independent isolation ofeach of these portions. One or both of the two portions with valvearrangements may be isolated, dependent on a signal from a controllerand/or sensor. In FIG. 5, isolation valves 540 are positioned in thevapor header 590 and liquid header 592 of the partitioned condenser 500.When isolation valves 540 are closed, the refrigerant is prevented fromflowing into the second condenser portion 530. When isolation valves 540are open, refrigerant is permitted to flow to both the first condenserportion 520 and the second condenser portion 530. The outlet flow 560leaving the partitioned condenser 500 comprises liquid refrigerantresulting from the heat exchange relationship with the heat transferfluid and the resultant phase change. The outlet flow 560 is thencirculated to the partitioned evaporator 200.

FIG. 6 illustrates a partitioned condenser 500 according to an alternateembodiment of the invention. Partitioned condenser 500 includes aplurality of heat transfer circuits 510. The heat transfer circuits 510are partitioned into a first condenser portion 520 and a secondcondenser portion 530. Although FIG. 6 shows two condenser portions, thepresent invention is not limited to two condenser portions. The presentinvention may include more than two condenser portions. Inlet flow 550is vaporous refrigerant from the compressor 130 that is split into tworefrigerant streams. The two refrigerant streams enter the partitionedcondenser 500 through two vapor headers 593 and 594 and travel into theheat transfer circuits 510. Heat transfer circuits 510 can enter into aheat exchange relationship with a heat transfer fluid such as air. Thetwo refrigerant streams then exit the partitioned condenser 500 throughtwo liquid headers 595 and 596. Isolation valves 540 are positioned onthe piping to the vapor header 594 and on the piping from the liquidheader 596 of the partitioned condenser 500. When isolation valves 540are closed, the refrigerant is prevented from flowing into the secondcondenser portion 530. When isolation valves 540 are open, refrigerantis permitted to flow to both the first condenser portion 520 and thesecond condenser portion 530. The outlet flow 560 leaving thepartitioned condenser 500 includes liquid refrigerant that is circulatedto the partitioned evaporator 200.

The system for controlling the refrigerant pressure of an airconditioning or heat pump unit according to the present inventionincludes an HVAC unit that can operate at lower ambient temperatures.The present invention involves a piping arrangement that partitions thecircuits within the condenser of a refrigeration system. The pipingarrangement includes valves positioned so that one or more of thecircuits within the condenser may be isolated from flow of refrigerant.The piping arrangement may be applied to a new system or may be appliedto an existing system. Applying the piping arrangement to the existingsystem has the advantage that it allows control of the refrigerantpressure without the addition of expensive piping, equipment and/orcontrols.

When the temperature around the partitioned condenser 500 decreases(e.g., when the outdoor temperature decreases), the system refrigerantpressure also decreases. To help increase refrigerant head pressure, thepresent invention uses the valves connected to the refrigerant circuits510 of the partitioned condenser 500 to isolate a portion of thepartitioned condenser 500 from flow of refrigerant. The portion of thepartitioned condenser 500 that is not isolated remains in the activecircuit and receives refrigerant. Because the refrigerant is onlypermitted to flow into a portion of the partitioned condenser 500, theheat transfer area and the corresponding amount of heat transfer isreduced. Therefore, less heat is removed from the refrigerant. Likewise,less heat is transferred to the first heat transfer fluid 150, therebymaintaining a higher refrigerant temperature. Additionally, because thetemperature of the refrigerant is higher, the corresponding pressure ofthe refrigerant is also higher. Therefore, the refrigerant pressure ofthe system is increased.

The piping arrangement of the partitioned condenser 500 of the presentinvention includes piping sufficient to isolate the one or more heattransfer circuits 510 within the condenser. In one embodiment, theisolation valves 540 are positioned inside the vapor header 590 of thepartitioned condenser 500. In an alternate embodiment, the isolationvalves 540 are positioned on piping upstream from the vapor headers 594of the partitioned condenser 500.

The lack of additional piping for both the partitioned evaporator 200and the partitioned condenser 500 also allows retrofitting of the systemof the present invention into existing systems. Because the systemutilizes the same components as existing systems, the system takes upapproximately the same volume as existing HVAC systems. Therefore, themethod and system of the present invention may be used in existingsystems whose piping is arranged according to the present invention.

FIG. 7 shows a refrigeration system 100 incorporating a partitionedevaporator 200 and a partitioned condenser 500 according to the presentinvention. FIG. 7 shows the refrigeration system 100, includingevaporator discharge line 145, blower 160, compressor 130, compressordischarge line 135, partitioned condenser 500, fan 170, condenserdischarge line 140, and first heat transfer fluid 150, substantially asdescribed above in the description of FIG. 1. FIG. 7 also shows thepartitioned evaporator 200, including first and second TXV valves 260and 265, isolation valve 250, check valve 255, first and seconddistributors 240 and 245, first and second discharge headers 270 and275, arranged as discussed above in the description of FIG. 2. Forillustration purposes, FIGS. 7-10 divides second heat transfer fluid 155flow into an inlet flow 710 and an outlet flow 715. The inlet flow 710,preferably air, flows into the partitioned evaporator 200 substantiallyevenly across the first and second evaporator portions 220 and 230.Blower 160 moves inlet flow 710. Although FIG. 7 depicts a blower, anyfluid moving means is suitable for moving the fluid across the first andsecond evaporator portions 220 and 230. The heat transfer fluid entersinto a heat exchange relationship with the first and second evaporatorportions 220 and 230 and exits the partitioned evaporator as outlet flow715. During cooling mode, refrigerant is circulated from the partitionedcondenser 500 to the partitioned evaporator 200, through the first andsecond evaporator portions 220 and 230 and to the compressor 130 throughevaporator discharge line 145. The inlet flow 710 of heat transfer fluidis cooled by both the first and second evaporator portions 220 and 230,providing outlet flow 715 of heat transfer fluid that has been cooled.During dehumidification mode, isolation valve 250 is closed, preventingflow of refrigerant into the first evaporator portion 220. The inletflow 710 is cooled and dehumidified by the second evaporator portion 230and is substantially untreated by the isolated first evaporator portion220. The outlet flow 715 is a mixture of the cooled, dehumidified airthat flowed through the second evaporator portion 230 and thesubstantially untreated air that flowed though the first evaporatorportion 220. The resultant outlet flow 715 is dehumidified air that isnot overcooled.

The partitioned condenser 500 shown in FIG. 7 is a partitioned condenserhaving two partitions, shown as the first and second condenser portions520 and 530. Although FIG. 7 shows two condenser portions, the presentinvention is not limited to two condenser portions. The presentinvention may include more than two condenser portions. The piping tothe partitioned condenser 500 includes isolation valves 540 on the inletside and the outlet side of the second condenser portion 530 inside thepartitioned condenser 500. Closing the isolation valves 540 prevents theflow of refrigerant to the second condenser portion 530. The isolationvalves 540 may be operated by a controller 720. One or more controllers720 facilitates the closing of isolation valves 540. The controller 720may receive inputs from pressure measuring or temperature measuringdevices and position the isolation valves 540, e.g., open or closed.When the pressure on the compressor suction line 145 from thepartitioned evaporator 200 to the compressor 130 reaches a predeterminedlevel, the isolation valves 540 can be closed to the second condenserportion 530. Once isolation valves 540 are closed, the refrigerant isonly permitted to flow through the first condenser portion 520. Becausethe refrigerant is only permitted to flow into first condenser portion520, the heat transfer area and the corresponding amount of heattransfer occurring in the partitioned condenser 500 is reduced.Therefore, less heat is removed from the refrigerant. Likewise, lessheat is transferred to the first heat transfer fluid 150, therebymaintaining a higher refrigerant temperature. Additionally, because thetemperature of the refrigerant is higher, the corresponding pressure ofthe refrigerant is also higher. Therefore, the refrigerant pressure ofthe system is increased.

FIG. 8 shows a refrigeration system according to an alternateembodiment. FIG. 8 includes substantially the same piping arrangement asFIG. 7. In addition, FIG. 8 has a line with a drain valve connecting thecondenser portion 530 to the suction of compressor 130. The refrigerantremaining in the second condenser portion 530 after isolation valves 540are closed may be stored in the second condenser portion 530 or may bedrawn into the refrigeration system 100 by opening drain valve 840 andpermitting the refrigerant in condenser portion 530 to be drawn into theactive system. Because the refrigerant from the isolated portion of thepartitioned condenser 500 adds to the amount of refrigerant per unitvolume of the refrigeration system 100, the pressure of the refrigerantin increased. Therefore, this addition of refrigerant into the systemfrom the isolated portion of the partitioned condenser 500 furtherassists in raising the system pressure.

FIG. 9 shows a refrigeration system 100 incorporating a partitionedevaporator 200 and a partitioned condenser 500 according to the presentinvention. FIG. 9 shows the refrigeration system including evaporatordischarge line 145, blower 160, compressor 130, compressor dischargeline 135, partitioned condenser 500, fan 170, condenser discharge line140, and first heat transfer fluid 150, substantially as described abovein the description of FIG. 7. In addition, FIG. 9 includes a 3-way valve910 and a discharge line 310. The 3-way valve 910 connects to the firstdischarge header 270 of the first evaporator portion 220, to theevaporator discharge line 145 and to the compressor discharge line 135.FIG. 9 also shows the partitioned evaporator 200 including first andsecond TXV valves 260 and 265, check valve 255, first and seconddistributors 240 and 245, first and second discharge headers 270 and275, arranged as discussed above in the description of FIG. 3. Heattransfer fluid flow 710, preferably air, flows into the partitionedevaporator 200 substantially evenly across the first and secondevaporator portions 220 and 230. A blower 160 moves heat transfer fluidflow 710. Although, FIG. 9 depicts a blower, any fluid moving system issuitable for moving the fluid across the first and second evaporatorportions 220 and 230. The inlet flow 710 enters into a heat exchangerelationship with the first and second evaporator portions 220 and 230and exits the partitioned evaporator as outlet flow 715. During coolingmode, the refrigerant is circulated from the partitioned condenser 500to the partitioned evaporator 200, through the first and secondevaporator portions 220 and 230 and to the compressor through evaporatordischarge line 145 and 3-way valve 910. The inlet flow 710 of heattransfer fluid is cooled by both the first and second evaporatorportions 220 and 230, providing outlet flow 715 of heat transfer fluidthat has been cooled. During dehumidification mode, hot gas refrigerantfrom the discharge of the compressor flows into the 3-way valve 910,which is opened to allow flow through the first discharge headerdischarge line 310 and into the first discharge header 270 of the firstevaporator portion 220. One or more controllers 720 facilitate thepositioning of 3-way valve 910. The controller 720 may receive inputsfrom pressure measuring or temperature measuring devices and positionthe 3-way valve 910. The hot gas refrigerant from the discharge of thecompressor 130 enters the refrigerant circuits 210 of the firstevaporator portion 220 and at least partially condenses to a liquid. Thecondensing refrigerant heats the first evaporator portion 220 and warmsthe inlet flow 710 to produce a higher temperature outlet flow 715. Therefrigerant, which is at least partially condensed, travels through thecheck valve 255 and combines with line 140 into the second evaporatorportion 230. The inlet flow 710 of heat transfer fluid is cooled anddehumidified by the second evaporator portion 230 and is heated by theisolated first evaporator portion 220, as the refrigerant gas is atleast partially condensed. The outlet flow 715 is a mixture of thecooled, dehumidified air that flowed through the second evaporatorportion 230 and the heated air that flowed though the first evaporatorportion 220. To summarize, the resultant outlet flow 715 is dehumidifiedair that is not overcooled. In cooling mode, first evaporator portion220 and second evaporator portion 230 of partitioned evaporator 200, actas evaporators. However, in dehumidification mode, first evaporatorportion 220 acts as a condenser, while second evaporator portion 230acts as an evaporator. The partitioned condenser 500 shown in FIG. 9operates substantially as described above in the discussion of FIG. 7.

FIG. 10 shows a refrigeration system 100 incorporating a partitionedevaporator 200 according to the present invention. FIG. 10 further showsthe refrigeration system 100 including evaporator discharge line 145,blower 160, compressor 130, compressor discharge line 135, partitionedcondenser 500, fan 170, condenser discharge line 140, and first heattransfer fluid 150, substantially as described above in the descriptionof FIG. 7. In addition, FIG. 10 includes one or both of a bypass valve440, and a flow restriction valve 430 on bypass line 410. Bypass line410 connects the compressor discharge line 135 of the compressor 130 tothe inlet of the first evaporator portion 220 between the first TXVvalve 260 and the first distributor 240. One or more controllers 720facilitate the positioning of isolation valves 540 and of the bypassvalve 440. The controller 720 may receive inputs from pressure measuringor temperature measuring devices and position the isolation valves 540and bypass valve 440, e.g., open or closed. FIG. 10 shows thepartitioned evaporator 200, including first and second TXV valves 260and 265, isolation valve 250, first and second distributors 240 and 245,and first and second discharge headers 270 and 275, arranged asdiscussed above in the description of FIG. 4. Inlet flow 710, preferablyair, flows into the partitioned evaporator 200 substantially evenlyacross the first and second portions 220 and 230. The inlet flow 710enters into a heat exchange relationship with the first and secondevaporator portions 220 and 230 and exits the partitioned evaporator asoutlet flow 715. During cooling mode, the refrigerant is circulated fromthe partitioned condenser 500 to the partitioned evaporator 200, throughthe first and second evaporator portions 220 and 230 and to thecompressor 130 through evaporator discharge line 145. The bypass valve440 and the flow restriction valve 430 are set to prevent flow ofrefrigerant through the bypass line 410. The inlet flow 710 of heattransfer fluid is cooled by both the first and second evaporatorportions 220 and 230, providing outlet flow 715 of heat transfer fluidthat has been cooled. During dehumidification mode, isolation valve 250is closed, preventing flow of refrigerant into the first evaporatorportion 220. The bypass valve 440 is opened and the flow restrictionvalve 430 is set to allow flow of refrigerant. Although FIG. 10 is shownwith both a bypass valve 440 and a flow restriction valve 430, eitherthe bypass valve 440 or flow restriction valve 430 may be removed fromthe bypass line 410, so long as the flow of the refrigerant may bestopped during cooling mode and permitted during dehumidification mode.Hot gas refrigerant from the discharge of the compressor 130 is thenallowed to flow from the compressor discharge line 135 through thebypass line 410 into the first distributor 240 and the first evaporatorportion 220. The hot gas refrigerant from the discharge of thecompressor 130 heats the first evaporator portion 220 and combines withthe outlet flow from the second evaporator portion 230 into theevaporator discharge line 145. The inlet flow 710 of heat transfer fluidis cooled and dehumidified by the second evaporator portion 230 and isheated by the hot gas from the discharge of the compressor in theisolated first evaporator portion 220. The outlet flow 715 is a mixtureof the cooled, dehumidified air that flowed through the secondevaporator portion 230 and the heated air that flowed though the firstevaporator portion 220. The resultant outlet flow 715 is dehumidifiedair that is not overcooled. The partitioned condenser 500 shown in FIG.10 operates substantially as described above in the discussion of FIG.7.

FIG. 11 illustrates a flow chart detailing a method of the presentinvention relating to head pressure control in a HVAC system for usewith the systems shown in FIGS. 7-10. The method includes adetermination of the minimum system head pressure, Pf, at step 1101. Theminimum head pressure is set to the desired operating pressure of therefrigeration system 100. The minimum head pressure is preferablygreater than the pressure corresponding to temperature of evaporatoricing. Evaporator icing may occur when the surface temperature of theevaporator and suction piping is less than 32° F. Pf is preferably thesystem high side pressure that results in saturated suction temperaturesabove freezing under most load conditions. For R22 refrigerant, atypical value of Pf is 180 psig. Subsequent to determining the minimumsystem head pressure, Pf, the actual system head pressure, Pm, ismeasured at step 1103. Any suitable pressure measurement method can beused for determining Pm. Preferably, the measurement takes place on aline between the TXV valve 265 and the compressor 130. Subsequent to themeasurement taken at step 1103, a determination of whether the measuredrefrigerant pressure is less than the minimum system head pressure, Pf,at step 1105. If the measured pressure of the refrigerant, Pm, is lessthan the pressure for evaporator freezing, which corresponds to Pf,(i.e., “YES” on the flowchart show in FIG. 11), isolation valve(s) 540are closed and refrigerant flow is blocked to one or more of therefrigerant circuits inside of the partitioned condenser 500 in step1107. If the measured pressure of the refrigerant, Pm, is greater thanthe minimum system head pressure, Pf, (i.e., “NO” on the flowchart shownin FIG. 11), a determination of whether the measure head pressure, Pm,is less than the system reset pressure, Pr as shown in step 1110. If themeasured pressure, Pm, is greater than the system reset Pressure, Pr,(i.e., “YES” on the flowchart shown in FIG. 11), the isolation valves540, if closed, will be opened. If the measured pressure, Pm, is lessthan the system reset pressure, Pr, (i.e. “NO” on the flowchart shown inFIG. 11), then no action will be taken regarding the isolation valves540. If open, the isolation valves 540 will remain open. If closed, theisolation valves 540 will remain closed. The value Pr-Pf represents apressure buffer for the system so that the isolation valves 540 will notbe inclined to open and close rapidly. The opening of the isolationvalves 540 in step 1109 allows refrigerant to flow to all refrigerantcircuits within the condenser. When the refrigerant flows through allthe refrigerant circuits 510 of the condenser, the heat transfer to thefirst heat transfer fluid 150 from the refrigerant is at a maximum. Ifthe isolation valves 540 are closed in step 1107, the refrigerant isonly permitted to flow through a portion of the partitioned condenser500. Each portion has a predetermined heat transfer surface area.Because the refrigerant is only permitted to flow into a portion of thecondenser and some portions are isolated, the heat transfer area and thecorresponding amount of heat transfer is reduced. Therefore, less heatis removed from the refrigerant. Likewise, less heat is transferred tothe first heat transfer fluid 150, thereby maintaining a higherrefrigerant temperature. Additionally, because the temperature of therefrigerant is higher, the corresponding pressure of the refrigerant isalso higher. Therefore, the refrigerant pressure of the system isincreased.

In the HVAC system according to the present invention, when the headpressure in the suction line 145 to the compressor 130 decreases, thetemperature of the refrigerant in the evaporator 110 likewise decreases.When the head pressure has decreased to a certain level, the partitionedevaporator 200 operates at temperatures that may result in icing of thepartitioned evaporator 200. Icing is a condition when the temperature atthe exterior of the refrigerant circuits of the evaporator issufficiently low to freeze water present in the heat transfer fluid. Inparticular, in a residential system, the heat transfer fluid istypically air and the water that freezes is humidity present in the air.The ice formed by the water frozen on the surface of the refrigerantcircuits eventually prevents the proper operation of the HVAC system byinhibiting heat transfer and/or damaging system components. This icinggenerally begins at refrigerant saturated suction temperatures fromabout 25° F. to about 32° F. In order to prevent the freezing of theevaporator, the pressure in the suction line 145 is preferablymaintained above the temperature that corresponds to the freezing pointof the partitioned evaporator 200.

In one method according to the invention, the pressure of therefrigerant is measured and compared to a predetermined pressure. Thepressure measurement may be taken from any point in the refrigerationsystem 100. However, the preferred point of measurement of refrigerantpressure is on the evaporator discharge line 145 to the compressor. Theevaporator discharge line 145 to the compressor also corresponds to theoutlet of the partitioned evaporator 200. The outlet of the partitionedevaporator 200 represents a low pressure point in the refrigerationsystem 100, due to the phase change of the refrigerant to a vaporresulting from the heat exchange relationship existing between therefrigerant and the second heat transfer fluid 155 in the partitionedevaporator 200. The predetermined pressure is preferably a pressure thatis greater than or equal to the pressure that corresponds to atemperature that results in icing at the partitioned evaporator 200.

FIG. 12 shows a control method according to one embodiment of thepresent invention for use with the system shown in FIGS. 7-8. The methodincludes a mode determination step 1210 where the operational mode ofthe system is determined or selected. The operational mode can beprovided by the controller and/or user, where the mode can either becooling only or require dehumidification. Examples of control systemsfor determination of the operational mode are described in furtherdetail below in the discussion of FIGS. 15 and 16. The method thenincludes a decisional step 1220 wherein it is determined whetherdehumidification is required or not. If the determination in step 1220is “NO” (i.e., no dehumidification required), then the method proceedsto opening step 1230 wherein the valve to the first evaporator portion220 is opened or remains open in step 1230. The opening of the firstevaporator portion 220 to the flow of refrigerant permits both the firstand second evaporator portions 220 and 230 to provide cooling to theinlet flow 710. If the decisional step 1220 is a “YES” (i.e.,dehumidification is required), then the valve to the first evaporatorportion 220 is closed or remains closed in step 1240. The closing of thefirst evaporator portion 220 to the flow of refrigerant allows the firstevaporator portion 220 to equilibrate at a temperature substantiallyequal to the temperature of the heat transfer fluid entering thepartitioned evaporator 200. After either the opening step 1230 or theclosing step 1240, the method returns to the determination step 1210 andthe method repeats.

Although FIG. 12 shows that the decisional step 1220 provides a “YES” or“NO” to steps 1230 or 1240, the method is not limited to an open orclosed isolation valve 250. A flow-restricting valve may also be used.The use of a flow-restricting valve allows the amount of flow into thefirst evaporator portion 220 to be varied. For example, the flowrestricting valve may be used in an operational mode that is open tofull flow, partially restricted flow or closed to flow, depending on thesignal from a controller. Controller 720, using inputs, such asrefrigerant temperature, heat transfer fluid temperatures, and humidityreadings, provides a signal to the restricting valve to determine theamount of refrigerant flow permitted through the isolation valve 250.

FIG. 13 shows another control method according to the present inventionfor use with the system shown in FIG. 9. The method includes a modedetermination step 1310 where the operational mode of the system isdetermined. As in the method shown in FIG. 12, the operational mode canbe provided by the controller and/or user, where the mode can either becooling only or dehumidification. Examples of control systems fordetermination of the operational mode are described in further detailbelow in the discussion of FIGS. 15 and 16. The method then includes adecisional step 1320 wherein it is determined whether dehumidificationis required or not. If the determination in step 1320 is “NO” (i.e., nodehumidification required), then the method proceeds to step 1330wherein the 3-way valve 910 is set to provide refrigerant flow from thedischarge line 310 of the evaporator portion 220 to the compressorsuction line 145. The setting of the 3-way valve 910 allows the flow ofrefrigerant to both the first and second evaporator portions 220 and 230to provide cooling to the inlet flow 710. If the decisional step 1320 isa “YES” (i.e., dehumidification is required), then the 3-way valve 910is set to provide refrigerant flow from the discharge of the compressorto the discharge line 310 of the evaporator portion 220. The hot gasrefrigerant from the discharge of the compressor 130 flows into thefirst evaporator portion 220 and provides heat to the first evaporatorportion 220. The directing of hot gas refrigerant to the firstevaporator portion 220 allows the first evaporator portion 220 toexchange heat with the heat transfer fluid 155 entering the partitionedevaporator 200. The inlet flow 155 of heat transfer fluid is cooled anddehumidified by the second evaporator portion 230 and is heated by heatexchange with the hot gas from the discharge of the compressor 130 inthe isolated first evaporator portion 220. The outlet flow 715 is amixture of the cooled, dehumidified air that flowed through the secondevaporator portion 230 and the heated air that flowed though the firstevaporator portion 220. The resultant outlet flow 715 is dehumidifiedair that is not overcooled. After either the 3-way valve 910 directingsteps 1330 or 1340, the method returns to the determination step 1310and the method repeats.

Although FIG. 13 shows that the decisional step 1320 provides a “YES” or“NO” to steps 1330 or 1340, the method is not limited to an open orclosed isolation valve 250. A flow restriction valve may also be used.The use of a flow restriction valve allows the amount of flow into thefirst evaporator portion 220 to be varied. For example, the flowrestriction valve may be used in an operational mode that is open tofull flow, partially restricted flow or closed to flow, depending on thesignal from controller 720. Alternatively, the flow into the firstevaporator portion 220 from the discharge of the compressor 130 indehumidification mode may be varied through use of the 3-way valve 910,depending on the signal from a controller. The 3-way valve 910 may alsoinclude flow restriction abilities that allow the flow of refrigerant tobe varied. A controller, using inputs, such as refrigerant temperature,heat transfer fluid temperatures, and humidity readings, provides asignal to the restriction valve or the 3-way valve 910 to determine theamount of refrigerant flow permitted through the isolation valve 250 orthe amount of hot gas refrigerant permitted through the first evaporatorportion 220.

FIG. 14 shows a control method according to the present invention foruse with the system shown in FIG. 10. The method includes a modedetermination step 1410 where the operational mode of the system isdetermined. As in the method shown in FIGS. 12 and 13, the operationalmode can be provided by controller 720 and/or user, where the mode caneither be cooling only or dehumidification. The method then includes adecisional step 1420 wherein it is determined whether dehumidificationis required or not. If the determination in step 1420 is “NO” (i.e., nodehumidification required), then the method proceeds to step 1430wherein the valve 250 to the first evaporator portion 220 is opened orremains open. After or concurrently with step 1430, a bypass line 410 isclosed from refrigerant flow in step 1340. The opening of the firstevaporator portion 220 and the closing of the bypass line 410 allow theflow of refrigerant to both the first and second evaporator portions 220and 230 to provide cooling to the inlet flow 710. If the decisional step1420 is a “YES” (i.e., dehumidification is required), then the valve tothe first evaporator portion 220 is closed or remains closed. After orconcurrently with step 1450, the bypass line 410 is opened to flow ofrefrigerant in step 1460. Hot gas refrigerant from the discharge of thecompressor 130 flows through the bypass 410 and into the firstevaporator portion 220 and provides heat to the first evaporator portion220. The closing of the first evaporator portion 220 to the flow ofrefrigerant from the condenser 130 and the directing of hot gasrefrigerant to the first evaporator portion 220 allows the firstevaporator portion 220 to exchange heat with the refrigerant circuits510 entering the partitioned evaporator 200. The inlet flow 710 of heattransfer fluid is cooled and dehumidified by the second evaporatorportion 230 and is heated by heat exchange with the hot gas from thedischarge of the compressor in the isolated first evaporator portion220. The outlet flow 715 is a mixture of the cooled, dehumidified airthat flowed through the second evaporator portion 230 and the heated airthat flowed though the first evaporator portion 220. The resultantoutlet flow 715 is dehumidified air that is not overcooled. After eitherthe bypass-closing step 1440 or the bypass-opening step 1460, the methodreturns to the determination step 1410 and the method repeats.

Although FIG. 14 shows that the decisional step 1420 provides a “YES” or“NO” to steps 1430 or 1450, the method is not limited to an open orclosed isolation valve 250. A flow restriction valve may also be used.The use of a flow restriction valve allows the amount of flow into thefirst evaporator portion 220 to be varied. For example, the flowrestriction valve may be used in an operational mode that is open tofull flow, partially restricted flow or closed to flow, depending on thesignal from controller 720. Additionally, the flow through the bypassline 410 may be varied through use of the bypass valve 440 and/or flowrestriction valve 430, depending on the signal from controller 720.Controller 720, using inputs, such as refrigerant temperature, heattransfer fluid temperatures, and humidity readings, provides a signal toisolation valve 250, bypass valve 440 and flow restriction valve 430 todetermine the amount of refrigerant flow permitted through the flowrestriction valve 430 in place of isolation valve 250 and the amount ofhot gas refrigerant permitted through the first evaporator portion 220.

FIG. 15 illustrates a control method according to the present inventionthat determines the operation mode of the partitioned evaporator 200.The determination of the operational mode is made through the use ofcontroller 720. This determination may be used in steps 1210, 1310 and1410 of FIGS. 12, 13 and 14, respectively. The determination takes placeby first sensing temperature and/or humidity in an enclosed space instep 1510. The temperature and/or humidity measurements are made for acontroller to determine whether the enclosed space requires cooling ordehumidification. The inputs from temperature sensors and humiditysensors are provided to controller 720 in step 1520, where thecontroller uses the sensed temperatures and/or humidity to determine theoperational mode. In step 1520, the controller determines whethercooling is required and whether dehumidification is required. In a firstdecisional step 1530, it is determined whether the controller hasdetermined that cooling is required. If the first decisional step 1530determines “YES”, cooling mode is required, the partitioned evaporator200 in the refrigeration system 100 is set to allow flow into all of therefrigerant circuits 210 in the partition evaporator 200 and cool acrossboth the first and second evaporator portions 220 and 230 in step 1540.In addition to cooling, cooling mode also performs dehumidification.However, in a cooling mode, the second heat transfer fluid is onlycooled and is not heated to increase the temperature of the second heattransfer fluid 155 once the second heat transfer fluid 155 travelsthrough the partitioned evaporator 200. If the first decisional step1530 determines “NO”, then a second decisional step 1550 is made. Thesecond decisional step 1550 determines whether the controller hasdetermined that dehumidification mode (i.e., dehumidification withoutovercooling) is required. If the second decisional step 1550 determines“YES”, dehumidification mode is required, the operational mode is set todehumidification in step 1560. If the second decisional step 1550determines “NO”, dehumidification mode is not required, the operationalmode is set to inactive and the system operates neither a cooling nor adehumidification cycle in step 1570.

FIG. 16 shows an alternate control method according to the presentinvention that determines the operation mode of a multiple refrigerantcircuit system. In the system controlled in FIG. 16, multiplerefrigerant systems 100 are utilized and one or more of the refrigerantsystems 100 include a partitioned evaporator 200 according to theinvention. The control method shown in FIG. 16 operates in a similarmanner to FIG. 15 in that the controller receives inputs fromtemperature and/or humidity sensors in step 1610 and determines theoperational mode of the system in step 1620. Likewise, if the firstdecisional step 1630 determines “NO”, then a second decisional step 1650is performed. The second decisional step 1670 determines whether thecontroller has determined that a dehumidification mode (i.e.,dehumidification without overcooling) is required. If the seconddecisional step 1670 determines “YES”, dehumidification mode isrequired, the operational mode is set to dehumidification in step 1680.If multiple refrigerant systems 100 are present, the controller 720independently determines which of the refrigerant systems 100 are activeor inactive, based upon temperature and/or humidity measurements. Whenmultiple refrigeration systems 100 are present, at least one refrigerantsystem 100 includes a partitioned evaporator 200. The controller 720independently determines which partitioned evaporator 200 is subject toisolation of the first evaporator portion 220, based upon temperatureand/or humidity measurements. However, if the second decisional step1670 determines “NO”, dehumidification is not required, the operationalmode is set to inactive and the system operates neither a cooling nor adehumidification cycle in step 1690. If the first decisional step 1630determines “YES”, cooling is required, a third decisional step 1640 isperformed. In the third decisional step 1640, a determination is made asto the number of stages to be activated in order to provide the cooling.Each stage has an evaporator capable of providing cooling to the secondheat transfer fluid 155. The greater the number of stages activated, thegreater the amount of cooling provided. At least one of the multiplerefrigerant circuits includes a partitioned evaporator 200. If thecontroller determines that the cooling demand only requires onerefrigerant system 100 to be active, one refrigerant system 100 will beused to cool second heat transfer fluid 155 in step 1650. When thepartitioned evaporator 200 is used to operate in cooling mode, thepartitioned evaporator 200 is configured to allow flow into all of therefrigerant circuits 210 in the partition evaporator 200 and cool acrossboth the first and second evaporator portions 220 and 230 in step 1660.If multiple partitioned evaporators 200 are present, all of therefrigerant circuits 210 in each of the partition evaporators 200 allowflow of refrigerant into both the first and second evaporator portions220 and 230 and cool the second heat transfer fluid 155.

The present invention is not limited to the control methods shown inFIGS. 11-16. The partitioned evaporator 200 and the partitionedcondenser 500 may be used in one or more refrigerant circuits ofmultiple refrigerant circuit systems, where the control of the reheatingcapabilities within the first evaporator portion 220 of the partitionedevaporator 200 and the head pressure control within the first condenserportion 520 may each be independently controlled to provide the desiredtemperature and/or humidity within the conditioned space and the desiredrefrigerant pressure within the system. Any combination of cooling,reheating, or modulation of combinations of cooling and reheating may beused with the present invention. In addition, operational modescontrolling the refrigerant pressure may be used in conjunction with thecooling and dehumidification modes of operation.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for dehumidification and controlling system pressure in arefrigeration system comprising the steps of: providing a refrigerationsystem having a compressor, a condenser and an evaporator connected in aclosed refrigerant loop, each of the condenser and evaporator having aplurality of refrigerant circuits; flowing a first heat transfer fluidover the condenser; flowing a second heat transfer fluid over theevaporator; controlling a flow of refrigerant in the plurality ofrefrigerant circuits in the condenser to control an amount of heattransfer between refrigerant in the condenser and the first heattransfer fluid; controlling a flow of refrigerant in the plurality ofrefrigerant circuits in the evaporator to control an amount of heattransfer between refrigerant in the evaporator and the second heattransfer fluid; isolating at least one of the refrigerant circuits ofthe condenser to provide a decreased amount of heat transfer area withinthe condenser and to increase refrigerant pressure within therefrigeration system when the refrigerant pressure within therefrigeration system is at or below a predetermined pressure; andconfiguring the plurality of refrigerant circuits of the evaporator toprovide dehumidification of the second heat transfer fluid withoutovercooling the second heat transfer fluid.
 2. The method of claim 1,further comprising drawing refrigerant from the at least one of thecircuits isolated from refrigerant flow in the condenser by fluidlyconnecting the isolated portion of the condenser to the suction of thecompressor and wherein refrigerant from the isolated portion of thecondenser is drawn into the refrigeration system to increase therefrigerant pressure.
 3. (canceled)
 4. The method of claim 1, furthercomprising measuring refrigerant pressure at a predetermined location inthe refrigeration system.
 5. The method of claim 1, the method furthercomprising: providing a first control valve fluidly connected to a firstset of circuits of the plurality of circuits of the evaporator, whereinthe first control valve controls flow of refrigerant to the first set ofcircuits of the evaporator; and providing a second control valve fluidlyconnected to a second set of circuits of the plurality of circuits ofthe evaporator, wherein the second refrigerant control valve controlsflow of refrigerant to the second set of circuits of the evaporator. 6.The method of claim 5, wherein the second control valve permits agreater amount of refrigerant flow than the first control valve and thefirst and second control valves are thermostatic expansion valves. 7.(canceled)
 8. The method of claim 5, the method further comprising:isolating the first set of circuits of the evaporator from flow ofrefrigerant from the condenser; providing at least a portion ofrefrigerant discharged from the compressor to the first set of circuitsof the evaporator without flowing through the condenser; and wherein thestep of providing at least a portion of refrigerant includes flowingrefrigerant from the compressor through a fluid connection to an inletof the first set of circuits of the evaporator.
 9. (canceled)
 10. Themethod of claim 8, wherein the step of providing at least a portion ofrefrigerant includes: connecting a discharge of the compressor to anoutlet of the first set of circuits of the evaporator, flowingrefrigerant from the compressor through a fluid connection to the firstset of circuits, the flow of refrigerant from the compressor through thefirst set of circuits of the evaporator being countercurrent to a flowof refrigerant in the second set of circuits of the evaporator,combining the flow of refrigerant through the first set of circuits withthe inlet flow of refrigerant of the second set of circuits of theevaporator; and further comprising condensing the refrigerant flowing inthe first set of circuits countercurrent to the flow of refrigerant inthe second set of circuits from a gas to a liquid, wherein the liquidflows into the second set of circuits of the evaporator.
 11. (canceled)12. A method for dehumidification and controlling refrigerant pressurein a heating, ventilation and air conditioning system comprising:providing a closed loop refrigerant system comprising a compressor, acondenser and an evaporator, each of the condenser and evaporator havinga plurality of refrigerant circuits configured and disposed to allowisolation of at least one of the refrigerant circuits from refrigerantflow; measuring refrigerant pressure at a predetermined location in therefrigeration system; determining an operational mode for therefrigeration cycle, the operational mode being a selected from thegroup consisting of cooling and dehumidification; isolating at least oneof the refrigeration circuits in the condenser from refrigerant flowwhen the measured pressure at the predetermined location is equal to orless than a predetermined pressure; isolating a first set of refrigerantcircuits in the evaporator from flow of refrigerant from the condenserwhen the operational mode is dehumidification; permitting flow ofrefrigerant from the condenser to both the first set of circuits and asecond set of refrigerant circuits in the evaporator when theoperational mode is cooling; and wherein the refrigerant pressure isincreased by isolation of at least one of the refrigerant circuits inthe condenser from refrigerant flow until the measured pressure isgreater than the predetermined pressure.
 13. The method of claim 12,further comprising dehumidifying a heat transfer fluid flowing over boththe first and second set of circuits when the operational mode isdehumidification.
 14. The method of claim 12, wherein the predeterminedlocation is the outlet of the evaporator and the predetermined pressureis a pressure corresponding to an icing condition of the evaporator. 15.(canceled)
 16. The method of claim 12, further comprising drawingrefrigerant from the at least one circuit isolated from refrigerant flowin the condenser by fluidly connecting a portion of the condenserincluding the at least one circuit isolated from refrigerant flow to thesuction of the compressor and wherein refrigerant from the portion ofthe condenser including the at least one circuit isolated fromrefrigerant flow is added to the refrigeration system to increase therefrigerant pressure.
 17. (canceled)
 18. The method of claim 12, furthercomprising: providing a first control valve fluidly connected to thefirst set of circuits of the plurality of circuits of the evaporator,wherein the first control valve controls flow of refrigerant to thefirst set of circuits of the evaporator; providing a second controlvalve fluidly connected to the second set of circuits of the pluralityof circuits of the evaporator, wherein the second refrigerant controlvalve controls flow of refrigerant to the second set of circuits of theevaporator; and wherein the second control valve permits a greateramount of refrigerant flow than the first control valve and the firstand second control valves are thermostatic expansion valves. 19.(canceled)
 20. (canceled)
 21. The method of claim 18, furthercomprising: providing at least a portion of refrigerant discharged fromthe compressor to the first set of circuits of the evaporator withoutfirst flowing through the condenser.
 22. The method of claim 21, whereinthe providing at least a portion of refrigerant step includes flowingrefrigerant from the compressor through a fluid connection to an inletof the first set of circuits of the evaporator.
 23. The method of claim21, wherein the providing at least a portion of refrigerant stepincludes: connecting a discharge of the compressor to an outlet of thefirst set of circuits of the evaporator; flowing refrigerant from thecompressor through a fluid connection to the first set of circuits, theflow of refrigerant from the compressor through the first set ofcircuits of the evaporator being countercurrent to the flow ofrefrigerant in the second set of circuits of the evaporator; combiningthe flow of refrigerant through the first set of circuits with an inletflow of refrigerant to the second set of circuits of the evaporator; andfurther comprising condensing the refrigerant flowing in the first setof circuits countercurrent to the flow of refrigerant in the second setof circuits from a gas to a liquid, wherein the liquid is flowed intothe second set of circuits of the evaporator.
 24. (canceled)
 25. Aheating, ventilation and air conditioning system comprising: acompressor; a condenser arrangement comprising: a plurality of circuitsarranged into a first and second portion; and a valve arrangementconfigured and disposed to isolate the first portion of the condenserarrangement when the refrigerant pressure is below a predeterminedpressure; and an evaporator arrangement comprising: a plurality ofcircuits arranged into a first and second portion; at least onedistributor configured to distribute and deliver refrigerant to eachcircuit of the plurality of circuits in the evaporator; and a valvearrangement configured and disposed to isolate the first portion of theevaporator arrangement from refrigerant flow in a dehumidificationoperation.
 26. The system of claim 25, further comprising: a firstcontrol valve fluidly connected to the first portion of the evaporator,wherein the first control valve controls flow of refrigerant to thefirst portion of the evaporator arrangement; a second control valvefluidly connected to the second portion of the evaporator arrangement,wherein the second control valve controls flow of refrigerant to thesecond portion of the evaporator arrangement; and wherein the secondcontrol valve permits a greater amount of refrigerant flow than thefirst control valve and the first and second control valves arethermostatic expansion valves.
 27. (canceled)
 28. (canceled)
 29. Thesystem of claim 25, further comprising a fluid connection to connect thecompressor to the first portion of the evaporator arrangement, the fluidconnection being configured to allow flow of at least a portion ofrefrigerant discharged from the compressor to the first portion of theevaporator arrangement without traveling through the condenserarrangement during a dehumidification operation.
 30. The system of claim29, wherein the fluid connection connects a discharge of the compressorto an inlet of the first portion of the evaporator arrangement.
 31. Thesystem of claim 29, wherein the fluid connection connects a discharge ofthe compressor to an outlet of the first portion of the evaporatorarrangement, wherein flow of refrigerant from the compressor through thefirst portion of the evaporator arrangement is permitted to flowcountercurrent to the flow of refrigerant in the second portion of theevaporator arrangement, refrigerant flowing in the first portion of theevaporator arrangement combines with refrigerant at an inlet of thesecond portion of the evaporator arrangement and the refrigerant flowingcountercurrent to the flow of refrigerant in the second portion of theevaporator arrangement condenses from a gas to a liquid and the liquidflows into the second portion of the evaporator arrangement. 32.(canceled)